RF diversity antenna coupling structure

ABSTRACT

AN RF diversity antenna coupling structure includes a differential low noise amplifier, a differential power amplifier, a first switch coupled to a first antenna, a second switch coupled to a second antenna, a first transformer, a second transformer, a transformer balun. The first transformer includes a primary winding and a secondary winding, wherein the primary winding of the first transformer is operably coupled to a differential output of the power amplifier, and wherein the secondary winding of the first transformer has a desired output impedance. The second transformer includes a primary winding and a secondary winding, wherein the primary winding of the second transformer is operably coupled to a differential input of the low noise amplifier, and wherein the secondary winding of the second transformer has a desired output impedance. The transformer balun includes a first winding and a second winding, wherein the first winding is operably coupled to the secondary windings of the first and second transformers, one node of the second winding is operably coupled to the first antenna and a second node of the second winding is operably coupled to the second antenna.

This patent application is claiming priority under 35 USC § 120 as acontinuing patent application of patent application entitled RF AntennaCoupling Structure, having a filing date of Oct. 10, 2003, and a Ser.No. 10/683,185 now U.S. Pat. No. 6,919,858.

BACKGROUND OF THE INVENTION

1. Technical Field of the Invention

This invention relates generally to communication systems and, moreparticularly, to radio receivers and transmitters used within suchcommunication systems.

2. Description of Related Art

Communication systems are known to support wireless and wire-linedcommunications between wireless and/or wire-lined communication devices.Such communication systems range from national and/or internationalcellular telephone systems to the Internet to point-to-point in-homewireless networks. Each type of communication system is constructed, andhence operates, in accordance with one or more communication standards.For instance, wireless communication systems may operate in accordancewith one or more standards including, but not limited to, IEEE 802.11,Bluetooth, advanced mobile phone services (AMPS), digital AMPS, globalsystem for mobile communications (GSM), code division multiple access(CDMA), local multi-point distribution systems (LMDS),multi-channel-multi-point distribution systems (MMDS), and/or variationsthereof.

Depending on the type of wireless communication system, a wirelesscommunication device, such as a cellular telephone, two-way radio,personal digital assistant (PDA), personal computer (PC), laptopcomputer, home entertainment equipment, et cetera, communicates directlyor indirectly with other wireless communication devices. For directcommunications (also known as point-to-point communications), theparticipating wireless communication devices tune their receivers andtransmitters to the same channel or multiple channels (e.g., one or moreof the plurality of radio frequency (RF) carriers of the wirelesscommunication system) and communicate over that channel or channels. Forindirect wireless communications, each wireless communication devicecommunicates directly with an associated base station (e.g., forcellular services) and/or an associated access point (e.g., for anin-home or in-building wireless network) via an assigned channel, orchannels. To complete a communication connection between the wirelesscommunication devices, the associated base stations and/or associatedaccess points communicate with each other directly, via a systemcontroller, via the public switch telephone network, via the internet,and/or via some other wide area network.

For each wireless communication device to participate in wirelesscommunications, it includes a built-in radio transceiver (i.e., receiverand transmitter) or is coupled to an associated radio transceiver (e.g.,a station for in-home and/or in-building wireless communicationnetworks, RF modem, etc.). As is known, the receiver receives RFsignals, demodulates the RF carrier frequency from the RF signals viaone or more intermediate frequency stages to produce baseband signals,and demodulates the baseband signals in accordance with a particularwireless communication standard to recapture the transmitted data. Thetransmitter converts data into RF signals by modulating the data inaccordance with the particular wireless communication standard toproduce baseband signals and mixes the baseband signals with an RFcarrier in one or more intermediate frequency stages to produce RFsignals.

To recapture data from RF signals, a receiver includes a low noiseamplifier, down conversion module and demodulation module. To convertdata into RF signals, a transmitter includes a power amplifier, anup-conversion module and a modulation module. For radio frequencyintegrated circuits (RFICs), it is desirable to provide the low noiseamplifier and the power amplifier with differential RF signals, insteadof single-ended RF signals, to improve noise performance and common moderejection. To convert received single-ended RF signals into differentialRF signals for a receiver, and to convert differential RF signals intosingle-ended signals for a transmitter, the receiver and/or thetransmitter includes a balun (i.e., a balanced/unbalanced transformer).

Until very recently, the baluns were off-chip, i.e., on the printedcircuit board, and were typically implemented in the form of micro-striplines. However, for semiconductor chip designs, it is desirable to placeRFIC baluns on-chip to reduce the cost of off-chip printed circuit boardcomponents. Recent attempts to integrate a balun onto a radio frequencyintegrated circuit have had limited success. For example, parallelwinding, inter-wound winding, overlay winding, single planar, squarewave winding, and concentrical spiral winding on-chip baluns have beentried with limited success. Each of these on-chip baluns suffers fromone or more of: low quality factor, (which causes the balun to have arelatively large noise figure and large energy loss); too low of acoupling coefficient (which results in the inductance value of the balunnot significantly dominating the parasitic capacitance making impedancematching more complex); asymmetrical geometry (which results indegradation of differential signals); and a relatively high impedanceground connection at the operating frequency.

Other problems exist for RFICs that include on-chip baluns. For example,a power amplifier (PA) and a low noise amplifier (LNA) have differentbalun requirements. An LNA balun should provide a high voltage gain witha low noise figure (NF), which is directly related to the quality factor(Q) of the balun. An LNA balun should also be inductive enough such thatonly on-chip capacitors are needed for impedance matching with theantenna and to provide the required voltage gain. A PA balun, however,is required to support large currents, which requires a large trackwidth of the transformer windings. The PA balun quality factor (Q)should also be high to provide high efficiency and high PA linearity andshould have enough current amplification to provide a large currentswing at the antenna output. The PA balun should also be inductiveenough such that only on-chip capacitors are needed for impedancematching with the antenna.

Therefore, a need exists for an integrated radio frequency (RF)integrated circuit that includes a symmetrical balun antenna couplingstructure that meets the differing operational requirements of both theLNA and the PA.

BRIEF SUMMARY OF THE INVENTION

The present invention is directed to apparatus and methods of operationthat are further described in the following Brief Description of theDrawings, the Detailed Description of the Invention, and the claims.Other features and advantages of the present invention will becomeapparent from the following detailed description of the invention madewith reference to the accompanying drawings.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

FIG. 1 illustrates a schematic block diagram of a wireless communicationsystem in accordance with the present invention;

FIG. 2 illustrates a schematic block diagram of a wireless communicationdevice in accordance with the present invention;

FIG. 3 illustrates a schematic block diagram of an antenna couplingstructure in accordance with the present invention; and

FIG. 4 illustrates a schematic block diagram of another antenna couplingstructure in accordance with the present invention.

DETAILED DESCRIPTION OF THE INVENTION

FIG. 1 illustrates a schematic block diagram of a communication system10 that includes a plurality of base stations and/or access points12–16, a plurality of wireless communication devices 18–32 and a networkhardware component 34. The wireless communication devices 18–32 may belaptop host computers 18 and 26, personal digital assistant hosts 20 and30, personal computer hosts 24 and 32 and/or cellular telephone hosts 22and 28. The details of the wireless communication devices will bedescribed in greater detail with reference to FIG. 2.

The base stations or access points 12 are operably coupled to thenetwork hardware 34 via local area network connections 36, 38 and 40.The network hardware 34, which may be a router, switch, bridge, modem,system controller, et cetera, provides a wide area network connection 42for the communication system 10. Each of the base stations or accesspoints 12–16 has an associated antenna or antenna array to communicatewith the wireless communication devices in its area. Typically, thewireless communication devices register with a particular base stationor access point 12–14 to receive services from the communication system10. For direct connections (i.e., point-to-point communications),wireless communication devices communicate directly via an allocatedchannel.

Typically, base stations are used for cellular telephone systems andlike-type systems, while access points are used for in-home orin-building wireless networks. Regardless of the particular type ofcommunication system, each wireless communication device includes abuilt-in radio and/or is coupled to a radio. The radio includes anintegrated RF front-end architecture as disclosed herein to enhanceperformance of radio frequency integrated circuits.

FIG. 2 illustrates a schematic block diagram of a wireless communicationdevice that includes the host device 18–32 and an associated radio 60.For cellular telephone hosts, the radio 60 is a built-in component. Forpersonal digital assistants hosts, laptop hosts, and/or personalcomputer hosts, the radio 60 may be built-in or an externally coupledcomponent.

As illustrated, the host device 18–32 includes a processing module 50,memory 52, radio interface 54, input interface 58 and output interface56. The processing module 50 and memory 52 execute the correspondinginstructions that are typically done by the host device. For example,for a cellular telephone host device, the processing module 50 performsthe corresponding communication functions in accordance with aparticular cellular telephone standard.

The radio interface 54 allows data to be received from and sent to theradio 60. For data received from the radio 60 (e.g., inbound data), theradio interface 54 provides the data to the processing module 50 forfurther processing and/or routing to the output interface 56. The outputinterface 56 provides connectivity to an output display device such as adisplay, monitor, speakers, et cetera, such that the received data maybe displayed. The radio interface 54 also provides outbound data fromthe processing module 50 to the radio 60. The processing module 50 mayreceive the outbound data from an input device such as a keyboard,keypad, microphone, et cetera, via the input interface 58 or generatethe data itself. For data received via the input interface 58, theprocessing module 50 may perform a corresponding host function on thedata and/or route it to the radio 60 via the radio interface 54.

Radio 60 includes a host interface 62, a receiver section, a transmittersection, local oscillation module 74, an antenna coupling structure 73,and an antenna 86. The receiver section includes a digital receiverprocessing module 64, analog-to-digital converter 66, filtering/gainmodule 68, down conversion module 70, low noise amplifier (LNA) 72, andat least a portion of memory 75. The transmitter section includes adigital transmitter processing module 76, digital-to-analog converter78, filtering/gain module 80, up-conversion module 82, power amplifier84, and at least a portion of memory 75. The antenna 86 may be a singleantenna that is shared by the transmit and receive paths via the antennacoupling structure 73 or multiple antennas to provide a diversityantenna arrangement. The antenna implementation will depend on theparticular standard to which the wireless communication device iscompliant.

The digital receiver processing module 64 and the digital transmitterprocessing module 76, in combination with operational instructionsstored in memory 75, execute digital receiver functions and digitaltransmitter functions, respectively. The digital receiver functionsinclude, but are not limited to, digital intermediate frequency tobaseband conversion, demodulation, constellation demapping, decoding,and/or descrambling. The digital transmitter functions include, but arenot limited to, scrambling, encoding, constellation mapping, modulation,and/or digital baseband to IF conversion. The digital receiver andtransmitter processing modules 64 and 76 may be implemented using ashared processing device, individual processing devices, or a pluralityof processing devices. Such a processing device may be a microprocessor,micro-controller, digital signal processor, microcomputer, centralprocessing unit, field programmable gate array, programmable logicdevice, state machine, logic circuitry, analog circuitry, digitalcircuitry, and/or any device that manipulates signals (analog and/ordigital) based on operational instructions. The memory 75 may be asingle memory device or a plurality of memory devices. Such a memorydevice may be a read-only memory, random access memory, volatile memory,non-volatile memory, static memory, dynamic memory, flash memory, and/orany device that stores digital information. Note that when theprocessing module 64 and/or 76 implements one or more of its functionsvia a state machine, analog circuitry, digital circuitry, and/or logiccircuitry, the memory storing the corresponding operational instructionsis embedded with the circuitry comprising the state machine, analogcircuitry, digital circuitry, and/or logic circuitry.

In operation, the radio 60 receives outbound data 94 from the hostdevice via the host interface 62. The host interface 62 routes theoutbound data 94 to the digital transmitter processing module 76, whichprocesses the outbound data 94 in accordance with a particular wirelesscommunication standard (e.g., IEEE 802.11a, IEEE 802.11b, Bluetooth, etcetera) to produce digital transmission formatted data 96. The digitaltransmission formatted data 96 will be a digital base-band signal or adigital low IF signal, where the low IF will be in the frequency rangeof zero to a few megahertz.

The digital-to-analog converter 78 converts the digital transmissionformatted data 96 from the digital domain to the analog domain. Thefiltering/gain module 80 filters and/or adjusts the gain of the analogsignal prior to providing it to the up-conversion module 82. Theup-conversion module 82 directly converts the analog baseband or low IFsignal into an RF signal based on a transmitter local oscillationprovided by local oscillation module 74. The power amplifier 84amplifies the RF signal to produce outbound RF signal 98 and routes theoutbound RF signal 98 to the antenna 86 via the antenna couplingstructure 73. The antenna 86 transmits the outbound RF signal 98 to atargeted device such as a base station, an access point and/or anotherwireless communication device.

The radio 60 also receives, via the antenna 86 and the antenna couplingstructure 73, an inbound RF signal 88, which can be transmitted by abase station, an access point, or another wireless communication device.The antenna coupling structure 73 provides the inbound RF signal 88 tothe LNA 72, which amplifies the signal 88 to produce an amplifiedinbound RF signal. The RF front-end 72 provides the amplified inbound RFsignal to the down conversion module 70, which directly converts theamplified inbound RF signal into an inbound low IF signal based on areceiver local oscillation provided by local oscillation module 74. Thedown conversion module 70 provides the inbound low IF signal to thefiltering/gain module 68, which filters and/or adjusts the gain of thesignal before providing it to the analog to digital converter 66.

The analog-to-digital converter 66 converts the filtered inbound low IFsignal from the analog domain to the digital domain to produce digitalreception formatted data 90. The digital receiver processing module 64decodes, descrambles, demaps, and/or demodulates the digital receptionformatted data 90 to recapture inbound data 92 in accordance with theparticular wireless communication standard being implemented by radio60. The host interface 62 provides the recaptured inbound data 92 to thehost device 18-32 via the radio interface 54.

As one of average skill in the art will appreciate, the radio may beimplemented in a variety of ways to receive RF signals and to transmitRF signals and may be implemented using a single integrated circuit ormultiple integrated circuits. Further, at least some of the modules ofthe radio 60 may be implemented on the same integrated circuit with atleast some of the modules of the host device 18-32. Regardless of howthe radio is implemented, the concepts of the present invention areapplicable.

FIG. 3 is a schematic block diagram of an antenna coupling structure 73operably coupled to a power amplifier 84, a low noise amplifier 72, andan antenna 86. The antenna coupling structure 73 includes a transformerbalun 104, a first transformer 100, and a second transformer 102. Thetransformer balun 104 may be constructed in accordance with theteachings of co-pending patent application entitled ON-CHIP TRANSFORMERBALUN, having a filing date of Jan. 23, 2002, and a Ser. No. 10/055,425,which is incorporated herein by reference and may further have aone-to-one turns ratio. The transformer balun 104 has a single-endedwinding that is couple to the antenna 86 and to ground and adifferential winding that is coupled to the second windings of both thefirst and second transformers 100 and 102.

As is further shown, the primary winding of the first transformer 100 iscoupled to the differential output of the power amplifier 84. The firsttransformer 100 includes a large track width of the transformer windingsto support the large currents of the power amplifier 84. In additions,the first transformer 100 has a high quality factor (Q) (e.g., greaterthan 10) to provide a highly efficiency and highly linear coupling tothe power amplifier 84. Further, the first transformer 100 includes again (e.g., two or more) to amplify the output current of the poweramplifier 84 to provide a large current swing at the antenna output.Still further, the primary winding of the first transformer 100 has adesired impedance of, for example 200 Ohms, to substantially match theoutput load impedance of the power amplifier 84. The secondary windingof the first transformer 100 has a desired impedance of, for example 50Ohms, to substantially match the impedance requirements of the antenna86.

As is also shown, the primary winding of the second transformer 102 iscoupled to the differential input of the low noise amplifier 72. Thesecond transformer 102 has a high voltage gain with a low noise figure(NF). The primary winding of the second transformer 100 has a desiredimpedance of, for example 1000 Ohms, to substantially match the inputimpedance requirements of the low noise amplifier 72. The secondarywinding of the second transformer 102 has a desired impedance of, forexample 50 Ohms, to substantially match the impedance requirements ofthe antenna 86.

In operation, the radio 60 is either transmitting or receiving RFsignals. Accordingly, the power amplifier 84 and the low noise amplifier72 each include an enable circuit, where, when the radio 60 istransmitting RF signals, the power amplifier 84 is on and the low noiseamplifier 72 is off and, when the radio is receiving RF signals, thepower amplifier 84 is off and the low noise amplifier 72 is on. Thus,when RF signals are being transmitted, the power amplifier 84 providesdifferential signals to the 1^(st) transformer 100, which adjusts theimpedance and current level of the differential signals and provides theadjusted differential signals to the transformer balun 104. Thetransformer balun 104 converts the differential signals intosingle-ended signals that are radiated by the antenna 86.

When RF signals are received, the transformer balun 104 converts thesingle-ended RF signals into differential signals. The secondtransformer 102 receives the differential signals and adjusts them andprovides the adjusted RF differential signals to the low noise amplifier102. With such an antenna structure, an integrated radio frequency (RF)integrated circuit that includes a symmetrical balun antenna couplingstructure that meets the differing operational requirements of both theLNA and the PA is achieved.

FIG. 4 is a schematic block diagram of another antenna couplingstructure 73 that includes the first transformer 100, the secondtransformer 102, the transformer balun 104, two antennas 86-1 and 86-2,and a pair of switches. The functionality of the first, second, andbalun transformers 100–104 is as previously discussed with reference toFIG. 3. This embodiment of the antenna coupling structure 73accommodates a diversity antenna arrangement. As is known, a diversityantenna arrangement includes two or more antennas that are physicallyspaced by a distance corresponding to a quarter wavelength, a halfwavelength, and/or a full wavelength of the RF signals. Based onreceived signal strength, one of the antennas is selected.

To provide the selection of one of the antennas, the transistors areenabled and disabled. For example, if antenna 86-1 is to be used, select1 signal is a logic high and select 2 signal is a logic low such thattransistor T2 is disabled and transistor T1 is enabled. If, however,antenna 86-2 is to be used, select 1 signal is a logic low and select 2signal is a logic high, thus enabling transistor T2 and disablingtransistor T1.

As one of average skill in the art will appreciate, the term“substantially” or “approximately”, as may be used herein, provides anindustry-accepted tolerance to its corresponding term. Such anindustry-accepted tolerance ranges from less than one percent to twentypercent and corresponds to, but is not limited to, component values,integrated circuit process variations, temperature variations, rise andfall times, and/or thermal noise. As one of average skill in the artwill further appreciate, the term “operably coupled”, as may be usedherein, includes direct coupling and indirect coupling via anothercomponent, element, circuit, or module where, for indirect coupling, theintervening component, element, circuit, or module does not modify theinformation of a signal but may adjust its current level, voltage level,and/or power level. As one of average skill in the art will alsoappreciate, inferred coupling (i.e., where one element is coupled toanother element by inference) includes direct and indirect couplingbetween two elements in the same manner as “operably coupled”. As one ofaverage skill in the art will further appreciate, the term “comparesfavorably”, as may be used herein, indicates that a comparison betweentwo or more elements, items, signals, etc., provides a desiredrelationship. For example, when the desired relationship is that signal1 has a greater magnitude than signal 2, a favorable comparison may beachieved when the magnitude of signal 1 is greater than that of signal 2or when the magnitude of signal 2 is less than that of signal 1.

The preceding discussion has presented an antenna coupling structurethat may be implemented on-chip or off-chip of a radio frequencyintegrated circuit (RFIC). By including the first and secondtransformers to accommodate for the different requirements of a poweramplifier and a low noise amplifier of a RFIC, a single symmetricaltransformer balun may be used. As one of average skill in the art willappreciate, other embodiments may be derived from the teachings of thepresent invention without deviating from the scope of the claims.

1. A radio frequency (RF) diversity antenna coupling structurecomprises: a differential low noise amplifier; a differential poweramplifier; a first switch coupled to a first antenna; a second switchcoupled to a second antenna; a first transformer having a primarywinding and a secondary winding, wherein the primary winding of thefirst transformer is operably coupled to a differential output of thepower amplifier, and wherein the secondary winding of the firsttransformer has a desired output impedance; a second transformer havinga primary winding and a secondary winding, wherein the primary windingof the second transformer is operably coupled to a differential input ofthe low noise amplifier, and wherein the secondary winding of the secondtransformer has a desired output impedance; and a transformer balunhaving a first winding and a second winding, wherein the first windingis operably coupled to the secondary windings of the first and secondtransformers, one node of the second winding is operably coupled to thefirst antenna and a second node of the second winding is operablycoupled to the second antenna.
 2. The RF diversity antenna couplingstructure of claim 1 wherein: the primary winding of the firsttransformer having a first impedance; and the primary windings of thesecond transformer having a second impedance, wherein the secondimpedance is much greater than the first impedance such that the firsttransformer provides a low drive impedance to substantially match outputimpedance of the power amplifier and the second transformer provides ahigh loud impedance to substantially match input impedance of the lownoise amplifier.
 3. The RF diversity antenna coupling structure of claim1, wherein the transformer balun further comprises a turns ratio ofone-to-one.
 4. RF diversity antenna coupling structure of claim 1wherein: the first transformer, the second transformer, and thetransformer balun being fabricated on a radio frequency integratedcircuit.
 5. The RF diversity antenna coupling structure of claim 1,wherein each of the first and second switches comprises a transistor.